Gillies Sharon L.

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Gillies
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Sharon L.
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  • Article
    Seasonal hydrology drives rapid shifts in the flux and composition of dissolved and particulate organic carbon and major and trace ions in the Fraser River, Canada
    (Copernicus Publications on behalf of the European Geosciences Union, 2015-10-01) Voss, Britta M. ; Peucker-Ehrenbrink, Bernhard ; Eglinton, Timothy I. ; Spencer, Robert G. M. ; Bulygina, Ekaterina ; Galy, Valier ; Lamborg, Carl H. ; Ganguli, Priya M. ; Montlucon, Daniel B. ; Marsh, Steve ; Gillies, Sharon L. ; Fanslau, Jenna ; Epp, A. ; Luymes, Rosalie
    Rapid changes in the volume and sources of discharge during the spring freshet lead to pronounced variations in biogeochemical properties in snowmelt-dominated river basins. We used daily sampling during the onset of the freshet in the Fraser River (southwestern Canada) in 2013 to identify rapid changes in the flux and composition of dissolved material, with a focus on dissolved organic matter (DOM). Previous time series sampling (at twice monthly frequency) of dissolved inorganic species in the Fraser River has revealed smooth seasonal transitions in concentrations of major ions and tracers of water and dissolved load sources between freshet and base flow periods. In contrast, daily sampling reveals a significant increase in dissolved organic carbon (DOC) concentration (200 to 550 μmol L−1) occurring over a matter of days, accompanied by a shift in DOM optical properties, indicating a transition towards higher molecular weight, more aromatic DOM composition. Comparable changes in DOM composition, but not concentration, occur at other times of year, underscoring the role of seasonal climatology in DOM cycling. A smaller data set of total and dissolved Hg concentrations also showed variability during the spring freshet period, although dissolved Hg dynamics appear to be driven by factors beyond DOM as characterized here. The time series records of DOC and particulate organic carbon (POC) concentrations indicate that the Fraser River exports 0.25–0.35 % of its annual basin net primary productivity. The snowmelt-dominated hydrology, forested land cover, and minimal reservoir impoundment of the Fraser River may influence the DOC yield of the basin, which is high relative to the nearby Columbia River and of similar magnitude to that of the Yukon River to the north. Anticipated warming and decreased snowfall due to climate changes in the region may cause an overall decrease in DOM flux from the Fraser River to the coastal ocean in coming decades
  • Preprint
    Tracing river chemistry in space and time : dissolved inorganic constituents of the Fraser River, Canada
    ( 2013-07-19) Voss, Britta M. ; Peucker-Ehrenbrink, Bernhard ; Eglinton, Timothy I. ; Fiske, Gregory J. ; Wang, Zhaohui Aleck ; Hoering, Katherine A. ; Montlucon, Daniel B. ; LeCroy, Chase ; Pal, Sharmila ; Marsh, Steven ; Gillies, Sharon L. ; Janmaat, Alida ; Bennett, Michelle ; Downey, Bryce ; Fanslau, Jenna ; Fraser, Helena ; Macklam-Harron, Garrett ; Martinec, Michelle ; Wiebe, Brayden
    The Fraser River basin in southwestern Canada bears unique geologic and climatic features which make it an ideal setting for investigating the origins, transformations and delivery to the coast of dissolved riverine loads under relatively pristine conditions. We present results from sampling campaigns over three years which demonstrate the lithologic and hydrologic controls on fluxes and isotope compositions of major dissolved inorganic runoff constituents (dissolved nutrients, major and trace elements, 87Sr/86Sr, δD). A time series record near the Fraser mouth allows us to generate new estimates of discharge-weighted concentrations and fluxes, and an overall chemical weathering rate of 32 t km-2 y-1. The seasonal variations in dissolved inorganic species are driven by changes in hydrology, which vary in timing across the basin. The time series record of dissolved 87Sr/86Sr is of particular interest, as a consistent shift between higher (“more radiogenic”) values during spring and summer and less radiogenic values in fall and winter demonstrates the seasonal variability in source contributions throughout the basin. This seasonal shift is also quite large (0.709 – 0.714), with a discharge-weighted annual average of 0.7120 (2 s.d. = 0.0003). We present a mixing model which predicts the seasonal evolution of dissolved 87Sr/86Sr based on tributary compositions and water discharge. This model highlights the importance of chemical weathering fluxes from the old sedimentary bedrock of headwater drainage regions, despite their relatively small contribution to the total water flux.